This invention relates to transparent, electrically conductive coatings, to windows made with such coatings, and to methods for their manufacture. More particularly, the invention relates to such coatings, windows, and methods for use in making the infrared (IR) and ultraviolet (UV) conductive windows.
Transparent conductive coatings and windows have application in a number of devices including resistance heating windows, electromagnetic interference (EMI) shielding, antistatic windows, and transparent electrodes. When used as infrared or UV transparent windows, it is desired that a substantial bandwidth of the energy pass with high transmittance while maintaining a low sheet resistance so as to block radiation which is outside the bandpass of the window.
In general, this invention provides spatially continuous conductive window or coating having an extended area and exhibiting low electrical resistivity and high optical transmission. The invention significantly enhances the overall responsivity of IR or UV detectors by providing electrical background radiation immunity without significant decrease in light intensity incident on the detectors protected by the window. The windows and coatings that are the subject of this invention must have a significant optical transmission bandwidth in order to be useful.
Induced transmission electrically conductive, transparent coatings and windows can be produced on a suitable substrate by sandwiching a thin metallic layer between dielectric thin films laid up on the substrate. While, low electrical resistivities have been achieved in certain prior art devices the optical transmission losses have not been acceptable. In those induced transmission configurations utilizing thin metallic films, low electrical resistivities and significant optical transmission have only been achieved for a narrow transmission bandwidth. The conductive layers used in prior art include noble metals and metal oxides Designs based on degenerate semiconductor materials, such as indium-tin-oxide (ITO), are applicable only to limited wavelength regions. Low electrical resistivity and high optical transmission have not been achieved with ITO for the infrared wavelengths.
While prior art coatings have been developed for the visible-to-near-infrared (.about.1 .mu.m) region, low electrical resistivity and high optical transmittance window criteria as set forth in this invention have not existed for mid-wavelength infrared applications (3-6 .mu.m). There is, therefore, a need for new optically transparent, conductive windows and coatings and methods for their manufacture.